Resistive Transduction
Physical deformation of semiconductor materials can be exploited to measure minute structural changes in mechanical bodies. This deformation effect, known as piezoresistive micro-strain, refers to the change in electrical resistivity of a silicon crystal when subjected to mechanical stress. The measurement capability is restricted to the elastic region of the silicon substrate to prevent permanent damage or hysteresis.
Bridge Configuration
Silicon strain gauges are typically arranged in a Wheatstone bridge circuit to convert the small resistance changes into a readable voltage output. As the structure undergoes deformation, the piezoresistive micro-strain alters the resistance of the bridge arms, causing a proportional output voltage. This bridge configuration maximizes the signal-to-noise ratio and provides first-order compensation for common-mode noise.
The sensitivity of the circuit depends on the excitation voltage applied to the bridge.
Temperature Interference
Semiconductor strain gauges are highly sensitive to thermal variations, which cause thermal expansion and change the carrier concentration in the silicon. This thermal effect introduces a drift that resembles a mechanical strain, which can distort the measurements if uncompensated.
Calibration Accuracy
Metrological labs qualify these sensors by applying known displacements using a precision micrometric stage and recording the bridge output. The resulting calibration curve establishes the gauge factor, which relates the resistivity change to the mechanical strain. If the output drifts from the established curve by more than the specified tolerance, the bridge must be re-calibrated.
This testing verifies that the sensor accurately captures the mechanical stress on the structure.
